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Message-ID: <20240119141529.GB23739@redhat.com>
Date: Fri, 19 Jan 2024 15:15:29 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Dylan Hatch <dylanbhatch@...gle.com>, Kees Cook <keescook@...omium.org>,
Frederic Weisbecker <frederic@...nel.org>,
"Joel Fernandes (Google)" <joel@...lfernandes.org>,
Ard Biesheuvel <ardb@...nel.org>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Vincent Whitchurch <vincent.whitchurch@...s.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Luis Chamberlain <mcgrof@...nel.org>,
Mike Christie <michael.christie@...cle.com>,
David Hildenbrand <david@...hat.com>,
Catalin Marinas <catalin.marinas@....com>,
Stefan Roesch <shr@...kernel.io>, Joey Gouly <joey.gouly@....com>,
Josh Triplett <josh@...htriplett.org>, Helge Deller <deller@....de>,
Ondrej Mosnacek <omosnace@...hat.com>,
Florent Revest <revest@...omium.org>,
Miguel Ojeda <ojeda@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] getrusage: use sig->stats_lock
Rather than lock_task_sighand(), sig->stats_lock was specifically designed
for this type of use. This way getrusage runs lockless in the likely case.
TODO:
- Change do_task_stat() to use sig->stats_lock too, then we can
remove spin_lock_irq(siglock) in wait_task_zombie().
- Turn sig->stats_lock into seqcount_rwlock_t, this way the
readers in the slow mode won't exclude each other. See
https://lore.kernel.org/all/20230913154907.GA26210@redhat.com/
- stats_lock has to disable irqs because ->siglock can be taken
in irq context, it would be very nice to change __exit_signal()
to avoid the siglock->stats_lock dependency.
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
kernel/sys.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/kernel/sys.c b/kernel/sys.c
index 70ad06ad852e..f8e543f1e38a 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1788,7 +1788,9 @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
unsigned long maxrss;
struct mm_struct *mm;
struct signal_struct *sig = p->signal;
+ unsigned int seq = 0;
+retry:
memset(r, 0, sizeof(*r));
utime = stime = 0;
maxrss = 0;
@@ -1800,8 +1802,7 @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
goto out_thread;
}
- if (!lock_task_sighand(p, &flags))
- return;
+ flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq);
switch (who) {
case RUSAGE_BOTH:
@@ -1829,14 +1830,23 @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
r->ru_oublock += sig->oublock;
if (maxrss < sig->maxrss)
maxrss = sig->maxrss;
+
+ rcu_read_lock();
__for_each_thread(sig, t)
accumulate_thread_rusage(t, r);
+ rcu_read_unlock();
+
break;
default:
BUG();
}
- unlock_task_sighand(p, &flags);
+
+ if (need_seqretry(&sig->stats_lock, seq)) {
+ seq = 1;
+ goto retry;
+ }
+ done_seqretry_irqrestore(&sig->stats_lock, seq, flags);
if (who == RUSAGE_CHILDREN)
goto out_children;
--
2.25.1.362.g51ebf55
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